1. Field of the Invention
The present invention is directed generally to the control of vibration in structures, and more particularly to the confinement of vibrational energy to selected portions of structures.
2. Description of Related Art
The suppression or control of vibration has an increasing importance in the design, manufacture, operation, maintenance, precision, and safety of structures and machinery. Engineering systems are subjected to numerous disturbances from either internal or external sources of vibration. Conventional methods for reducing the effect of vibration take several forms, and may be classified into the three general categories, viz. 1) isolation, e.g. the use of rubber shock mounts, 2) absorption (redirection), and 3) suppression (dissipation).
Conventional active vibration control methods utilize sensors, signal processing, actuators, and power sources to produce forces or strains in the system that counteract the vibration or to effectively increase the dissipation in a system.
xe2x80x9cSmartxe2x80x9d materials and structures have extended the range of active, as well as passive, vibration control mechanisms, where the term xe2x80x9csmartxe2x80x9d refers to materials or structures that respond to environmental or operational conditions by altering their material, geometric, or operational properties. Such a response may be triggered both with and without additional control mechanisms (such as a sensory and feed-back loop). Examples of smart materials include piezoceramics, shape memory alloys, electrostrictive and magnetostrictive materials, rheological and magnetological fluids.
Although active control methods have been shown to be effective in some limited applications, their drawbacks are emphasized by a reliance on computationally complex control algorithms, high numbers of sensors and high actuator power requirements, and continuous monitoring and feedback or feed-forward mechanisms. These drawbacks have demonstrated the need for an alternative or additional approach to vibration control. Additionally, semi-active control techniques reduce only the requirement on continuous actuation but their development and implementation has not yet progressed as far as fully active control or passive control.
It is important for the economic operation and practical implementation of active and passive vibration control technologies that the number of controlled regions and controlling components be reduced to achieve the vibration control objectives more effectively and efficiently.
There are common features between the above methods. First, they are designed to control vibrations in a reactive manner. All of these methods assume (or necessitate) that excessive vibration energy is present in all regions of a structure which are to be controlled. The vibration control mechanism then acts upon this vibration energy to suppress vibration. Second, these methods are all designed to be most effective in a certain frequency range. Isolators, absorbers, and dampers, whether active or passive, must be tuned to a specific frequency range of interest. Active cancellation methods are also limited in their effective frequency range by the speed of signal processing and activator response time requirements. Third, these methods are designed without regard to the distribution of vibrational energy throughout the system.
Therefore, there is a need for a method of controlling vibrational energy in a system which is proactively designed into the system, and which takes account of total energy distribution throughout the system. There is also a need to expand the frequency range over which vibrational energy is controlled. Further, economic considerations drive a need to reduce the number of controlled regions and controlling components and to reduce the complexity of active vibration control systems.
Generally, the present invention relates to a method of controlling the distribution of vibrational energy throughout a structure, a structural component, or a machine, hereafter referred to as the xe2x80x9csystemxe2x80x9d. The method, known as vibration control by confinement (VCC), includes selecting a confinement region in a vibrating member in which the vibrational energy is to be confined. A device for confining the vibrational energy is positioned on the vibrating member at a determined position. The vibration confinement device has effective translational stiffnesses, effective torsional stiffnesses and an effective mass which result in the application of translational, torsional and inertial forces to the system. These translational, torsional and inertial forces result in confining vibrational energy to the vibration confinement region. The extent of the vibration confinement region is determined by the location at which the effective translational, torsional and inertial forces are applied to the system.
The VCC approach to vibration control targets the root cause of vibration-related problems, the flow of vibration energy within a system. By controlling the flow of vibration energy, several advantages over conventional vibration control approaches may be realized. The VCC approach allows the reduction of vibration levels to a greater degree than either conventional passive or active control methods, overcomes frequency range limitations of conventional control methods, reduces system vibration response for all types of disturbances, and brings selected regions of a system to acceptable vibration levels more quickly.
Advantages of implementing vibrational control by confinement (VCC) include confining undesired vibrations to specified regions of the structure, thereby achieving a higher level of vibration suppression throughout the remaining regions or components of the structure. Additionally, VCC permits better optimization of vibration control systems to make them more economically attractive.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.